PROJECT SUMMARY/ABSTRACT Approximately 1.4 million older adults live in nursing homes. The majority of nursing home residents have moderate or severe cognitive impairment. Cognitive impairment can negatively impact a variety of health outcomes. The federal Precision Medicine initiative highlights the need to identify specific subgroups that respond to tailored interventions and ultimately provide clinicians with knowledge and tools necessary to select treatments that work best for the unique needs of an individual patient. Using a comprehensive longitudinal dataset, the proposed research will employ a novel analytic approach to evaluate the role of cognitive impairment on a selected common condition in nursing home residents -- depression. The heterogeneous symptoms of depression can indeed impair cognitive functioning. Depression treatment has been identified by the National Institute on Aging as a way to potentially prevent cognitive impairment and promote healthy aging. We propose using the national federally-mandated Minimum Data Set (MDS) 3.0 linked to Medicare Part A and D claims data to: 1) identify subgroups of depression among nursing home residents and evaluate if these subgroups differ by cognitive impairment status; 2) characterize how these subgroups change throughout the nursing home stay and estimate the extent to which these changes differ by level of cognitive impairment; and 3) estimate the extent to which antidepressant treatment effects vary across identified subgroups of depression and levels of cognitive impairment. Latent class and latent transition analyses with causal inference methods will be used. This proposal addresses the National Institute on Aging?s strategic research directions on how to improve the health and well-being of adults as they age by developing interventions for preventing or reducing the burden of age-related conditions (Goal C) and increasing knowledge of the aging brain and neurodegeneration (Goal D). This exploratory research will provide valuable information to inform precision medicine efforts and improve the processes of care to a population most in need.